Ignition device



Patented Nov. 8, 1938 UNITED STATES PATENT OFF-ICE IGNI'rIoN DEVICE Application July 1s, 193s, semi No. 90,846

1': claim. (cina-169) 'This invention relates to ignition apparatus, and more particularly to' spark plugs adapted for use in internal combustion engines.

The adaptability of ceramic materials, such 5 as porcelain, for use as means for mounting the center electrode of a spark plug and for insulating said electrode from the metallic body or grounded portion of the plug, has long been known to the art. Spark plugs heretofore prol vided employing ceramic materials have not,

however, been suitable for use in heavy duty engines, such as in aircraft engines, because the same have not been capable of withstanding the v intense heat and wide temperature changes to l which they are subjected. This difficulty has been due in part to the low heat conductivity from the ceramic portion of the plug to the metallic parts thereof, and in part to detrimental effects resulting from the fact that the various parts of the plug have diiIerent coefncients of thermal expansion. The low heat conductivity has been enhancedl in these plugs at running temperatures by a film of hot gases of combustion which escape from the cylinder through a space between the ceramic and metallic portions of the plug, said space being created by reason of the different coemcients of expansion of the two materials. Spark plugs employing mica insulation have proved durable so in heavy duty engines, but ceramic plugs possess the distinct advantage that flash-overs, such asgoccur in mica plugs and result in inefilcient operation,'are substantially avoided.

It is accordingly an object of the present invention to provide a novel spark plug in which ceramic materials are employed as insulation.

Another object of the invention is to provide a novel ceramic spark plug which is so constructed that leakage of gases therethrough is minimized.

vA'further object is to provide a novel spark plug wherein heat conduction from the center portions thereof to the outer air-cooled parts is greatly enhanced, thereby substantially increasiing the rate of heat dissipation and prolonging the life of the plug.

Still anotherobject is to provide a novel method of fabricating a spark plugin which ceramic insulation is employed.

A still further Objectis to provide a spark plug in which the detrimental effects of the different rates and extent of expansion and contraction of the various materials employed due to temperature changes is minimized.

/u Another object is to providea novel spark plug which may be reliably and efficiently used in heavy duty engines during long periods of con'L stant use without danger of failure.

'I'he above and further objects and novel features of the invention will more fully appear from the following detailed description when the 'same is taken in connection with. the accompanying drawing. It is to be expressly understood, however, that the drawing is for the purpose of illustration only and is not designed 10 as a denition of the limits ofthe invention, referenee being primarily had for this latter purpose to the appended claims.

In the drawing, wherein like reference characters refer to'like parts throughout the several l5 views,

Fig. 1 is a side elevation, partly in section and with parts broken away, showing one form of the invention embodied in a radio shielded spark plug;

Fig. 2 is a detail sectional view on an enlarged scale of a portion of the spark plug illustrated in Fig..1; and.

Fig. 3 is a side elevation, partly in section, of a second embodiment of the invention.

One embodiment 'of the invention is illus-'- trated; by way of example only, ,in Fig. 1 as being embodied in a radio shle ded spark plug suitable for use on aircraft ngines. In the formlshown, said spark plug comprises a tubu- 30 lar metallic body 5' having external threads 6 adjacent the lower end thereof, whereby the same may be threaded into a suitable opening in an internal combustion engine cylinder (not shown). lSaid body is preferably constructed 35 of a metal having a high melting point. An internal shoulder 1 is provided in body 5 for supporting a center electrode and insulation assembly to be fully described hereafter, and one or more electrodes l are soldered to thelcwer A0 end of the body and extend radially and inwardly from the inner periphery thereof. Shoulder 1 is preferably angular, the upper surface thereof being tapered downwardly from the inner wall of the body. If desired, the upwardly 45 extending cylindrical or barrel vportion 5a of body 5 may' be formed separately and threaded into the lower portion of the body, a common practice inthe art today.`

Heretofore ceramic insulating bodies carrylng the center electrodev of a spark plug have been supported by. an internal shoulder in the body and held therein by means of a gland nut threaded into said body and engaging an external shoulder on the insulator. In this type f of plug, the ceramic insulator does not have iirm engagement with the body and gland nut except alongcomparatively narrow annular surfaces which engage gaskets interposed between said insulator and body for the purpose of preventing gas leakage. Heat conduction between surfaces which merely engage each other is always low and is particularly low when the surfaces are not irmly engaged, thus leaving an appreciable air space between the same. Furthermore, when a plug of the above type is heated during use, the expansion of the metallic parts of the plug is greater than that of the insulation, thereby permitting leakage of hot gases which in escaping form a heat insulating film between the insulator and the metallic body. The heat conduction from the insulator is not only thus materially reduced but the surface o1' the insulator` which is subjected to heating by the hot gases is materially increased. Overheating and failure of the ceramic `insulator invariably results when plugs of the above type are employed in heavy duty engines. 1 A` novel method and means are provided by the present invention for obviating the above dimculties and disadvantages encountered in ceramic plugs heretofore produced. In the embodiment of the invention shown in Fig. 1, a tubular ceramic insulator 9, made of porcelain or other suitable substance and having a reduced inside diameter at the lower end thereof, is supported in body S on shoulder l, a soft metallic gasket 8a being interposed between said shoulder and a tapered external shoulden on the insulator. The upper end o f the latter extends to a point adjacent the upper end of barrel 5a, which is turned inwardly to form a ange I3 that engages the top of the insulator i'or holding the same in the body and in ilrm engagement with gasket 8a.

For the purpose of enhancing heat conduction from insulator 9 to the air-cooledouter walls of body 5, 5a and to obviate the leakage and accumulation of hot gases of combustion between said insulator and body, novel heat conducting and sealing means are provided. As illustrated, the outside diameter of that portion of insulator 9.

. which extends above shoulder l, is somewhat less than the inside diameterfof body 5, 5a, thereby forming an annular space or chamber I which communicates with the exterior of the plug through one or more openings II in the wall of body 5. The outer surface of insulator 9, which forms the inner wall of annular chamber I Il, is glazed in any suitable manner, for example, by

spraying a mixture of'pulverized glass and water thereon and then firing the same in a kiln to form o ne or more coats or lms of glaze i2. For

a purpose to appear hereafter, a plurality of nl msof glaze Ilo to Ild maybe applied to insulator 9. the inner iilm I2a (Fig. 2) vhaving a coeflicient of thermal expansion comparable to that of ceramic insulator body l. The coeiilcients of expansion o f layers I'2b, I2c, and Ild increase progressively in the order named and thutofy layer I2d is comparable to the` coemcient of px"- pension of the metal tov which the same isfused in a manner to be next described. L After securing the glazed insulator l, I2 in body l, .la inthe manner above described or in any other suitable manner I l, said chamber is lled or partially filled with` a comparatively soft, plastic metal' having high heat conductivity and adapted to be fused or welded to the glazed insulator and to haves. close,

engagement with the walls of body l, ia.

Inthe form shown, a liner Il, of some suitable metal, such as aluminum or copper, is provided. The metal is preferably placed in chamber Il in tlaked or powdered form, hereinafter referred to as pulverized, either through openings II or through the upper end of the body, before the margin of barrel a is turned inwardly to form the holding flange I3. I'he assembled plug is then baked, the temperature being raised to a point such that the iiaked or powdered metal is melted'and the glazed coatings I2 are rendered soft or tacky. The metal and glaze are thus caused to fuse or weld together and form a composite mass through which heat conduction is sccelerated. I'he metal liner I4 thus formed also assumes a iirmv engagement with the walls of body 5, 5a.

Gas leakage through the plug is thus substantially eliminated, thereby removing one of the chief causes of poor heat conduction from the insulator to the body of the plug and, at the same time, providing a structure through which heat conduction is extremely good. Furthermore, the provision of a plurality of coats of glaze having progressively increasing coemcients of thermal expansion ranging from the coeiilcient of expansion of insulator 9 to that of metal liner I4 prevents the adjacent layers of materials from breaking away from one another due to excessive differences in changes of lengths of said materials when the plug is subjected to wide temperature changes in use.

Liner I4 may also .be provided by pouring molten metal, such as aluminum, copper, or alloys thereof, into chamber I0 through opening II, the temperature of the metal being such that the outer surface of glaze nlm I2 is rendered tacky by Acontact therewith, thereby causing a fusing of the metal and glaze.' When the latter method is employed, insulator 9, I2 is preferably coated, before assembly of the body and insulator, with a thin metallic coating which may be fused or welded to glaze coating I2 by applying the same thereto in molten form while the glaze is sumciently heated to become tach. Thus, when the molten metal is poured through opening Ii, it is only necessary that the temperature of the same be suillcient to cause fusion or welding between the same and the previously applied metal coat- Insulator 9 is provided with a central bore in which a center electrode I l is closely fitted and cemented by means of any suitable electrode cement now employed in the manufacture of spark plugs. The lower end of electrode il projects below the lower end of insulator 8 and extends between grounded electrod'... Prefer# ably, a metallic sleeve II, made of copper or other suitable metal having .high heat conductivity, surrounds the upper end of electrode I I and is threaded into an enlarged bore in the central portion `of insulator l, said sleeve being silver soldered to electrode i! at ila.V "I'he extreme upper end `of said electrode is counterbored and peened outwardly into engagement with s conducting washer I'I which rests on an internal shoulder-in insulator I. Y

Electrode I5' is ldlpted to be connected to l.

A suitable lsource of high tension electric energy to provide aV chamber a (not shown) by means ofu an insulated cable Il which extends through a metallic shielding elbow Il and connected in some suitable msnner to s conducting rod n. The meer u mp;

Ported in ,an insulating sleeve II that'extends intotheupperenlargedboreofinsulstorl. The

leither large or small quantities.

lower end of rod 2li has electrical engagement with electrode I5 through a coil spring 22 which maybe secured to the lower end of rod 20. This electrical engagement is maintained by a nut 23 which is threaded onto the upper end of barrel 5a and engages an external flange 24 on the lower end of elbow I9 to hold the latter in position.

A second embodiment of the invention is illustrated. in Fig. 3, wherein a ceramic insulator 25 is mounted in a novel manner in a tubular metallic body comprising a' member 26 and a gland nut 21. Body member 25 is externally threaded at the lower end thereof for mounting in an internal combusv n engine cylinder and is provided with grounded electrodes 28. Nut 21 is externally threaded for cooperative engagement with internal threads provided in the enlarged bore at the upper end of member 26.

Interposed between insulator 25 and body 26, 21 and extending into the annular recess between the lower bevelled end of nut 21 and a bevelled internal shoulder or seat 29 in member 2B is a soft metallic ring 30, which is fused or Welded to insulator 25. Ring 30 may be fused to the insulator in substantially the same manner as above described in connection with the embodiment of Fig. l. One or more films of glaze 3I are first applied to an annular surface of the insulator, and the latter is then placed in a properly formed sand or clay mold. The cavity in the mold around the glazed surface, which cavity has the desired shape of ring 30, is filled with-.powdered or fiaked aluminum or copper, for example, and the same baked or fired to melt the pulverized metal and cause the same to fuse to the glazed surface 3| which is rendered tacky by the heat. If desired, metal to form ring 30 may be poured into the mold in molten form.

Insulator 25 is supported in body 26, 21 by clamping ring between nut 21 and shoulder 29, sufficient pressure being exerted on the ring by said nut to form a gas-tight joint andone through which heat conduction ishigh in comparison to joints heretofore employed. Insulator 25, being thus supported, is free to expand and contract longitudinally relative to body 25, 21 during use without affecting the gas tightness of the plug but, at the same time, greatly reducing the probability of damage to the insulator that has heretofore resulted by reason of the different coefficients of expansion of the several parts of the plug andthe varying rates at which the parts become heated in use, as well as the varying rates at which said parts are permitted to cool after being so heated.

`Insulator 25 is provided with a central bore for receiving a center electrode 32 and an externally threaded sleeve 33 which is silver soldered to the upper end of said electrode. A nut 34 ls threaded on the upper end of electrode 32 for holding an electric terminal (not shown) in,

engagement therewith.

There is thus provided a novel spark plug wherein gas leakage is minimized and the rate of heat conduction away from the parts subjected to the greatest heat is materially enhanced. Additionally, a spark plug is provided wherein the detrimental effects which heretofore resulted from the' varying extent and rates of expansion and contraction of the several parts of the plug are obviated. The plug provided is simple in construction, the same comprising a comparatively few number of parts, and may be readily and inexpensively manufactured in A plug is also provided wherein the necessity for gaskets herey tofore employed is eliminated.

Although only a single embodiment of the invention has been illustrated and described, it is to be expressly understood that the `same is not limited thereto, but that various changes may be made therein. For example, the materials specified for glaze coatings I2, liner I4, and ring 30 are exemplary only and are specified merely as preferable. Also, chamber I2 may, of course, be wholly or only partially filled, as shown, with the metallic matrix constituting liner I4. Other changes may also be made in the design and arrangement of parts illustrated without departing from the spirit and scope of the invention, as will now be understood by those skilled in the art. For a definition of the limits of the invention, reference will be hadprimarily to the appended claims.

What is claimed is:

1. In a spark plug. a metallic body, an elecv trode, an insulator interposed between said body an insulator supported interiorly of said body.'

Vand metallic means fused to said insulator and interposed between the sameand said body.

3. A spark plug comprising a tubular body portion having an internal .annular shoulder, an insulator in said body supported by said shoulder and having a portion of the surface thereof glazed, and means fused to said glazed surface and contacting said body.

4. In a spark plug, a metallic body, an insulator supported interiorly of sa'id body and having a portion of the surface thereof glazed, and metallic means fused to said glazed surface and interposed between said insulator and said body.

5. A spark plug comprising a metallic tubular body having an internal shoulder, a tubular insulator supported on said shoulder, the outside diameter thereof being less than the inside diameter of said body, a metallic gasket interposed between said shoulder and insulator, means for holding said insulator in the body, and a metallic liner completely filling the lower portion of the annular space between said insulator and body.

f 6. A spark plug comprising a metallicl tubular body having an internal shoulder, a tubular insulator supported by said shoulder, a coating of glaze on a portion of the surface of said insulator, and a metallic liner fused to said coating andengaging the inner walls of said body.

7. A spark plug comprising a metallic tubular body, a tubular insulator in said body, the diameter of said insulator being less than the inside diameter of said body, and a metallic liner fused to the outer surface of said insulator and engaging the inner walls of said body.

8. A spark plug comprising a metallic tubular body having an internal shoulder, a tubular insulator supported n said shoulder, the diameter of said insulator being less than the bore of said body, means for holding said .insulator in the body, and a metallic liner interposed between said insulator and body, said liner being positioned therein while in molten form.

9. In a Aspark plug, a tubular body comprising a member having an internal shoulder and a 'member threaded into said first member, a tubusaid insulator, said ring being clamped between said shoulder and said second-named member whereby said insulator is supported in said body.

10. In a spark plug, a tubular body comprising a member having an internal shoulder and a member threaded into said iirst member, a tubular insulator extending centrally of said body,

and a radially extending metallic ring fused to said insulator and extending into the annular groove formed between said second-named member and said shoulder.

l1. In a spark plug, a tubular body comprising a member having an internal shoulder and a gland nut threaded .into said member, a tubular insulator extending centrally,\ of said body, a coating of glaze on a portion of the surface of said insulator, and an annular metallic ring fused to said glazed surface, said ring being adapted to rest on said shoulder to support said insulator, the same being pressed against said shoulder by said nut.

12. The method of fabricating a spark. plug, which includes glazing the surface of a ceramic insulator, mounting said insulator in a tubular metallic body to provide a chamber between said body and insulator, filling all or a portion of saidchamber with metal, and fusing said metal to said glazed surface. y

13. The method of fabricating a spark plug. which includes glazing the surface of an insulator, confining pulverized metal in contact with said glazed surface, and heating the same to fuse said metal to said glazed surface.

14. The method of fabricating a spark plug, which includes gazing the surface of an insulator, fusing a coating of metal to said glazed surface, mounting the insulator in a metallic body to provide a chamber between said body and insulator, injecting molten metal into said chainber, and permitting said molten metal to cool.

15. In an ignition device, a ceramic insulator, a glaze coating on a portion of the surface of said insulator, and a metallic coating fused to said glaze coating.

16. In a spark plug, a metallic body comprising a pair of separable members, a ceramic insulator in said body, a metallic ring fused to said insulator and adapted to be held betv .n said members for supporting the insulator. f v

17. A spark plug comprising a metallic body,

an insulator, and metallic means fused to said insulator for 'supporting the same in said body.

ROY- T. HURLEY. 

